To the best of my knowledge, all packages are compliant with the latest
version of Debian policy (v4.1.1), but I did not check them one-by-one.
Apply change to 905 packages, using:
$ dht mass-change "Declare compliance with Debian policy 4.1.1" \
'sed -i -e "s/^Standards-Version:.*/Standards-Version: 4.1.1/" debian/control' p/*

This is mostly to work around problems with `setup test` on architectures
with insufficient threading support in GHC
(https://github.com/haskell/cabal/issues/2398). This matches a patch also
in the ghc package, but we need it here as well for the sake of packages
that build-depend on libghc-cabal-dev.